This application is a 371 of PCT/JP00/0660, filed Oct. 5, 2000.
1. Technical Field
The present invention relates to improvements in a wire electric discharge machining method and a wire electric discharge machine in which electric power is supplied between a wire electrode and a workpiece so that a workpiece is machined by electric discharge energy generated between the wire electrode and the workpiece.
2. Background Art
Electric discharge machining has acquired a steadfast position as a technique for machining metallic dies and others. Therefore, electric discharge machining has been widely used for machining metallic dies in the automobile industry, electric appliance industry and semiconductor industry.
FIGS. 8A to 8E are schematic illustrations for explaining a mechanism of electric discharge machining. In the drawing, reference numeral 1 is an electrode, reference numeral 2 is a workpiece, reference numeral 3 is an arc column, reference numeral 4 is a machining solution and reference numeral 5 represents chips created in the process of electric discharge machining. While the following processes (a) to (e), which correspond to FIGS. 8A to 8E, are being repeatedly conducted, removal machining is conducted on the workpiece 2 by electric discharge. Each process proceeds as follows.
(a) Formation of the arc column 3 by the generation of electric discharge
(b) Local melt of the workpiece and vaporization of the machining solution 4 by the thermal energy of electric discharge
(c) Generation of vaporizing explosive power by the machining solution 4
(d) Dispersion of the melted portion (chips 5)
(e) Cooling, coagulation and restoration of insulation between the electrodes executed by the machining solution
The present invention relates to wire electric discharge machining used for gouging, cutting and so forth. Concerning the technique of wire electric discharge machining, there is a strong demand for higher accuracy. For example, when metallic dies used in the field of manufacturing semiconductors, the dimensional accuracy of which is high, are machined, it is necessary to conduct machining with high accuracy of 1 to 2 xcexcm.
FIGS. 9A to 9C are schematic illustrations showing an example of the wire electric discharge machining process. In the drawing, reference numeral 1a is a wire electrode, reference numeral 2 is a workpiece, reference numeral 4a is water which is a machining solution, and reference numeral 6 is an initial hole. FIG. 9A shows a first cut process which is a rough machining process, FIG. 9B shows a second cut process which is an intermediate finishing process to be conducted after the rough machining process, and FIG. 9C shows a third cut process which is a final finishing process.
An example of the first cut process shown in FIG. 9A shows a gouging process in which the wire electrode 1a is threaded into the initial hole 6 and the workpiece 2 is gouged by electric discharge. In the case of the first cut process described above, since the surface roughness and the accuracy are finished in the later process, it is unnecessary to machine the workpiece with high accuracy, and it is important to increase a rate of machining so as to enhance the productivity. In order to enhance the rate of wire electric discharge machining, water 4a is jetted out between the electrodes so that chips can be effectively ejected from between the electrodes. In order to spray water 4a between the electrodes uniformly and prevent the breaking of the wire electrode 1a, a method is adopted in which water 4a is stored up in a machining tank and the workpiece 2 is dipped in the water 4a. As described above, a means for supplying a machining solution between the electrodes is used.
In the conventional wire electric discharge machining method described above, the second cut process (shown in FIG. 9B), which is conducted after the first cut process (shown in FIG. 9A), and the third cut process (shown in FIG. 9C), are conducted in the water 4a which is a machining solution.
FIG. 10 is a view showing an example of the waveforms of voltage and current between the electrodes. In the view, V is a voltage between the electrodes, and I is a current between the electrodes, and t is time. A state at time T1 in FIG. 10 shows that voltage is impressed between the wire electrode 1a and the workpiece 2. When voltage is impressed between the electrodes, an attraction force acts between the positive and the negative polarity. By this electrostatic force, the wire electrode 1a, the rigidity of which is low, is drawn onto the workpiece 2 side, which could be a cause of vibration of the wire electrode 1a. Due to the vibration, it becomes difficult to conduct electric discharge machining with high accuracy.
A state at time T2 in FIG. 10 shows that vaporizing explosive power is generated in the machining solution by electric discharge energy (for example, shown in FIG. 8C). The wire electrode 1a is given a strong force by the vaporizing explosive power created in the machining solution in a direction opposite to the workpiece 2, and vibration is generated. Due to the vibration, irregularities are caused on the profile of the workpiece 2, which impairs the dimensional accuracy.
In the industry of semiconductors in which wire electric discharge machining is utilized, the following cases are increased. For example, in the case of machining metallic dies of IC lead frames, very high accuracy and very smooth surface roughness are required when a workpiece is machined, the dimensional accuracy of which is 1 xcexcm, and the surface roughness of which is not more than 1 xcexcm Rmax. In the case where high accuracy and smooth surface roughness are required as described above, remarkable problems are caused by the aforementioned vibration of the wire electrode.
The present invention has been accomplished to solve the above problems. It is an object of the present invention to provide a wire electric discharge machining method and a wire electric discharge machine suitable for conducting electric discharge machining with high accuracy and reliability.
The present invention provides a wire electric discharge machining method in which electric discharge is generated between a wire electrode and a workpiece so as to machine the workpiece by electric discharge, comprising the steps of: machining the workpiece while at least two types of machining in three types of machining including machining in a machining solution, machining in mist and machining in gas are being combined with each other; and removing at least one of the liquid of the machining solution adhering to the workpiece and the liquid of the machining solution having a possibility that the liquid drips onto a machining face of the workpiece at least at one of the point of time before the start of machining except for the machining conducted in the machining solution and the point of time after the operation of an automatic wire connecting device for conducting an automatic wire connection while the wire electrode is being held by a water column.
The present invention provides a wire electric discharge machine in which electric discharge is generated between a wire electrode and a workpiece so as to machine the workpiece by electric discharge, comprising: at least one of the machining solution supply means for supplying a machining solution between the electrodes and the mist supply means for supplying mist between the electrodes; pressurized gas jetting means for removing at least one of the liquid of the machining solution adhering to the workpiece and the liquid of the machining solution having a possibility that the liquid drips onto a machining face of the workpiece at least at one of the point of time before the start of machining except for the machining conducted in the machining solution and the point of time after the operation of an automatic wire connecting device for conducting an automatic wire connection while the wire electrode is being held by a water column; and positioning means for positioning by relatively moving the workpiece and the pressurized gas jetting means.
Also, the present invention provides a wire electric discharge machine in which electric discharge is generated between a wire electrode and a workpiece so as to machine the workpiece by electric discharge, comprising: at least two of the machining solution supply means for supplying a machining solution between the electrodes, the mist supply means for supplying mist between the electrodes and the gas supply means for supplying gas between the electrodes; pressurized gas jetting means for removing at least one of the liquid of the machining solution adhering to the workpiece and the liquid of the machining solution having a possibility that the liquid drips onto a machining face of the workpiece at least at one of the point of time before the start of machining except for the machining conducted in the machining solution and the point of time after the operation of an automatic wire connecting device for conducting an automatic wire connection while the wire electrode is being held by a water column; and positioning means for positioning by relatively moving the workpiece and the pressurized gas jetting means.
Also, the present invention provides a wire electric discharge machine in which the pressurized gas jetting means is a machining solution nozzle capable of changing over a fluid to be supplied between the machining solution and the pressurized gas.
Also, the present invention provides wire electric discharge machine in which a relative movement of the workpiece with the pressurized gas jetting means made by the positioning means is conducted according to a program for machining the workpiece.
The wire electric discharge machining method and wire electric discharge machine of the present invention are composed as described above, and it is possible to combine the machining in a machining solution, the machining in mist and the machining in gas with each other, and further it is possible to utilize the essential characteristic of each machining. Therefore, it is possible to provide an effect that a highly reliable wire electric discharge machining method and wire electric discharge machine, which are appropriately used for machining with high accuracy, can be obtained.